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dd: use seek for stdin skip when possible #9821

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dd: use seek for stdin skip when possible #9821

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33 changes: 27 additions & 6 deletions src/uu/dd/src/dd.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -258,16 +258,37 @@ impl Source {
return Ok(len);
}
}
match io::copy(&mut f.take(n), &mut io::sink()) {
Ok(m) if m < n => {
// Try seek first; fall back to read if not seekable
match n.try_into().ok().map(|n| f.seek(SeekFrom::Current(n))) {
Some(Ok(pos)) => {
if pos > f.metadata().map(|m| m.len()).unwrap_or(u64::MAX) {
show_error!(
"{}",
translate!("dd-error-cannot-skip-offset", "file" => "standard input")
);
}
Ok(pos)
}
Some(Err(e)) if e.raw_os_error() == Some(libc::ESPIPE) => {
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@asder8215 asder8215 Dec 24, 2025 •
edited
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I usually prefer using e.kind() over e.raw_os_error(). Is there a reason to use libc::ESPIPE over std::io::NotSeekable?

Edit: Realized that std::io::NotSeekable might not be the equivalent code for this on documentation

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@asder8215 asder8215 Dec 24, 2025

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Wait, is lib::ESPIPE not equivalently supported through Rust's ErrorKind?

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@ChrisDryden ChrisDryden Dec 24, 2025

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I'm unsure what the difference is between the two, I can try it out now to see if it still passes all of the tests

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@asder8215 asder8215 Dec 24, 2025

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There isn't a difference between using libc's errors or Rust's ErrorKind; I just thought it looks a bit more idiomatic relying on Rust's ErrorKind over libc's errno values.

But I think this is one of those cases where libc::ESPIPE might fall under Rust's std::io::Other error, which isn't that descriptive.

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@ChrisDryden ChrisDryden Dec 24, 2025

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Yea this one is not the equivalent, the stable ErrorKind does not have a matching variant for this use case.

match io::copy(&mut f.take(n), &mut io::sink()) {
Ok(m) if m < n => {
show_error!(
"{}",
translate!("dd-error-cannot-skip-offset", "file" => "standard input")
);
Ok(m)
}
other => other,
}
}
_ => {
show_error!(
"{}",
translate!("dd-error-cannot-skip-offset", "file" => "standard input")
translate!("dd-error-cannot-skip-invalid", "file" => "standard input")
);
Ok(m)
set_exit_code(1);
Ok(0)
}
Ok(m) => Ok(m),
Err(e) => Err(e),
}
}
Self::File(f) => f.seek(SeekFrom::Current(n.try_into().unwrap())),
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